Date of Award
Master of Science (MS)
Eric W. Peterson
Manual and high frequency observations (n = 535) of chloride (Cl-), bromide (Br-), nitrate (NO3-N), sodium (Na+), calcium (Ca2+), and potassium (K+) of stream and tile-drain waters were conducted in an urban-agricultural watershed (8% urban, 87% agriculture) to investigate the importance of stormflow to Cl- transport and to explore potential differences in the signature of Cl- originating from an urban source as compared to an agricultural source. The study was conducted in Evergreen Lake Watershed (ELW) located in central Illinois. Manual samplings were conducted on a weekly interval from February 2018 to February 2019 at three station along Six Mile Creek (SMC), the main drainage of ELW. All storm events were sampled at high frequency at the most downstream station while select storm events were sampled at an upstream station to compare how export changes along the stream. Nearly all surface water and tile water samples had Cl- concentrations above the calculated background threshold of 18 mg/l. Mann-Whitney U test show ratios of Cl- to Br- (p = 0.045), NO3-N (p < 0.0001), Ca2+ (p < 0.0001), and Na+ (p < 0.0001) to statistically significantly different between urban and agricultural waters. Cl- ratios indicate that road salt is the dominant source of Cl- in ELW while KCl fertilizer is an important secondary source. Total Cl- export during the study period was 777055.8 kg. Storm events are vital to Cl- export in ELW, accounting for 57.64% of total Cl- load during only 19% of the study period. The importance of storm events varies seasonally with winter and spring storms accounting for nearly half of total Cl- export, while summer and fall storm event account for only 10% of total export. Results imply two periods of Cl- flushing in ELW. The first is associated with flushing of road salt from impervious surfaces following the cold season and second is associated with flushing salt build up from the dry season. When road salt is present on watershed surfaces increased discharge always corresponds with increased Cl- load. During storm events when road salt is not present on watershed surfaces increased in discharge corresponds with increased Cl- load at lower discharges. At higher discharges the relationship reaches an asymptote where further increases in discharge do not correspond with increased Cl- load. Tile drains do not appear to impact the asymptotic behavior of Cl- load-discharge relationship. This study demonstrates that deicing in watersheds where urban land use is minimal can have a profound impact on Cl- dynamics.
Oberhelman, Andrew, "Chloride Signature and Transport in an Urban-Agricultural Watershed" (2019). Theses and Dissertations. 1128.